Periodontal diseases are one of the most common bacterial infections of humans and impose a significant burden on the health care system. One of the predominant pathogens in periodontal disease is the gram- negative anaerobe P. gingivalis. However, P. gingivalis can also inhabit the oral cavity in the absence of overt disease and can participate in a balanced interaction with host cells. Epithelial cells that line the gingival crevice function both as a physical barrier and as sensors of microbial colonization. The outcome of the interaction between P. gingivalis and gingival epithelial cells, therefore, makes a significant contribution to the degree of equilibrium between host and microbe, and to overall gingival health status. P. gingivalis can manipulate epithelial cell signal transduction pathways in order to direct entry into the host cell and to reprogram host innate immunity. One of the effector molecules of P. gingivalis is the HAD family serine phosphatase, SerB. The goal of this proposal is to define the mechanism of action of SerB as it relates to uptake of the organism by gingival epithelial cells and modulation of innate immunity. Firstly, the ability of SerB to dephosphorylate and activate cofilin will be examined. Cofilin regulates actin dynamics through mediating the disassembly of actin filaments, and our hypothesis is that activation of cofilin by SerB is required for P. gingivalis entry. This will be tested through up and down regulation of cofilin activity by siRNA and transfections with activation-altered cofilin. Secondly, we shall determine the signaling pathways modulated by SerB that converge on suppression of the chemokine IL-8. The participation of MEK and NF-?B will be investigated by blotting, mobility shift assays and dominant positive and negative mutations. Finally, we shall characterize the interconnectivity between SerB-induced cytoskeletal signaling and IL-8 suppression, by manipulation of actin filament structure and MEK activation status. These studies will provide a detailed molecular analysis of the targeting of host signal transduction by a specific effector phosphatase of P. gingivalis. Ultimately, the knowledge gained could be developed into strategies that could be utilized to intervene in the P. gingivalis-epithelial cell interaction to ensure that the outcome is non-harmful to the host.